A tree of arithmetic or logical operations is composed of arithmetic or logical operations organized according to a tree structure. The tree structure includes a plurality of nodes, each node having at least two inputs and one output. Each node corresponds to an arithmetic or logical operation between data received on its input and offers the result of the arithmetic or logical operation on its output.
The tree structure may be divided into successive levels:                a first level composed of leaf nodes,        several intermediate levels, each intermediate level being composed of nodes having inputs directly connected to the outputs of nodes of the same preceding level, and        a root level having a root node.        
The computation of such a tree of operations requires a plurality of iterations. During an iteration all the operations corresponding to nodes of a same level are executed.
Typically, a method of computing at least a first tree and a second tree of arithmetic or logical operations on a microprocessor comprising at least n parallel processing elements includes:                a) executing n arithmetic or logical operations of a first iteration of the first tree in parallel using the n processing elements, then        b) executing m arithmetic or logical operations in parallel between the results of the first iteration, using m processing elements chosen from the n processing elements used for the computation of the first iteration, the other n−m processing element being unused for the computation of the second iteration, where m is an integer strictly smaller than n.        
Once the first operation tree has been computed, the processing elements are configured to process, in a similar way, the second operation tree.
This is an ineffective way of using a microprocessor having parallel processing elements because during the computation of the second iteration of the first operation tree, some processing elements remain unused.
An example of a microprocessor comprising n parallel processing elements is described in U.S. 2003/0088603 by Andrew Paul Wallace.